1. Field of the Invention
The present invention is broadly concerned with an improved method for the fractionation of gluten to yield gliadin and glutenin. More particularly, the invention pertains to such a fractionation method which is preferably essentially free of alcohol in order to avoid the problems of alcohol recovery and environmental pollution typical of present separation techniques. The method hereof involves initially forming a dispersion of gluten in an aqueous acidic medium in the presence of a reducing agent (e.g., sodium metabisulfite) operable to break disulfide bonds in the gluten protein, followed by elevating the pH of the dispersion and causing precipitation of glutenin leaving gliadin suspended in the dispersion; the glutenin and gliadin fractions can then be separated. Use of reducing agents in the gluten dispersion lowers the viscosity of the dispersion and greatly facilitates the desired fractionation.
2. Description of the Prior Art
Wheat gluten can readily be isolated from wheat flour simply by working wheat flour dough under a stream of water. The suspendible starch fraction of the flour is washed away, leaving substantially water insoluble wheat gluten normally containing about 75% by weight protein, 8% by weight lipid, and with the remainder being ash, fiber and residual starch. Isolated wheat gluten can then be separated into its primary proteinaceous components, gliadin and glutenin.
Gliadin is a single-chained protein having an average molecular weight of about 30,000-40,000, with an isoelectric of pH 4.0-5.0. Gliadin proteins are extremely sticky when hydrated and have little or no resistance to extension. Gliadin is responsible for giving gluten dough its characteristic cohesiveness. Glutenin is a larger, multi-chained protein with an average molecular weight of about 3,000,000 ranging from 100,000 to several million. The isoelectric pH of glutenin is about 6.5-7.0. Glutenin is resistant to extension and is responsible for the elasticity of gluten dough.
Gliadin and glutenin are premium products, when available. Gliadin is known to improve the freeze-thaw stability of frozen dough and also improves microwave stability. This product is also used as an all-natural chewing gum base replacer, a pharmaceutical binder, and improves the texture and mouth feel of pasta products and has been found to improve cosmetic products. Glutenin has been used as a dough strengthening agent for bakery products and has shown potential in meat replacement products.
Generally, wheat gluten is fractionated into gliadin and glutenin proteins by initially solubilizing the gluten in dilute acid and then adding ethanol until a 70% solution is achieved. The solution is then neutralized with base and left to stand overnight at refrigeration temperatures. The ethanol-soluble gliadins go into solution while the glutenins precipitate out. Final separation involves decantation or centrifugation to yield the separate proteinaceous fractions. Although alcohol methods of the type described are effective for fractionating gliadin and glutenin in laboratory situations, these techniques are not practical for high volume, commercial manufacturing. Specifically, use of the high concentrations of ethanol can be dangerous owing to potential explosion hazards, and moreover may present an environmental hazard. Attempts at using lower concentrations of ethanol, while seemingly an improvement, ultimately present the same problems as the conventional high alcohol concentration techniques.
There is accordingly a real and unsatisfied need in the art for an improved gluten fractionation process which will yield high grade glutenin and gliadin products without the need for ethanol as a separation solvent.